Telephone-exchange system



Sept. 25, 1923. 1,468,853

A. H. ADAMS v TELEPHONE EXCHANGE SYSTEM Filed May 13 1920 6 Sheets-Sheet 1 Sept. 25, 1923.

A. H. ADAMS TELEPHONE EXCHANGE SYSTEM Filed May 13 1920 6 Sheets-Sheet 2 (1 H mm; to: i f Jfidams 440,1

E @QRQMQMW QEQQNW ARTHUR H. ADAMS, OF G ALIQN, OHIO.

-Excuses: SYST'.

Application filed May is,

To all whom it may concern:

Be it known that I, ARTHUR H. ADAMS, a' citizen of the United States, residing at Galion, in the county of Crawford and State of Ohio, have invented a certain new and useful Improvement in Telephone- Exchange Systems, of which the following is a specifi- "cation.

This invention relates to telephone and other electrical signaling systems, and particularly to telephone systems in which ma- .chine switches are employed for establishing connections.

The principal object of the invention is to increase the efficiency of trunks and machine switches of telephone exchange systems.

For the purpose of analyzing the characteristics of this invention, it will be first explained how it affects the trunking and op eration of any well-known telephone system.

Let us consider, for example, a telephone system having a capacity of ten thousand lines and in which machine switches are employed. Such switches are at present usu- ;ally arranged to perform a primary movement to select a desired one out of a plurality of groups of lines, and a secondary movement to select or choose an idle one of the selected group of lines. However, it should be noted at the outset that the invention is not limited to systems or switches of any particular size, type or character.

At present, in such a telephone system, if each switch has a capacity of one hundred lines, first selectors, second selectors and connectors are necessary for establishing connections. The first and second selectors are interconnected by trunks bearing the various thousands numerical designations the trunks interconnecting the second selectors and connectors are differentiated from each other by the hundreds numerical digits of line numbers, and the connectors are connected direct with the subscribers lines. A calling line may be connected to a called line only through trunks, the numerical designation of which corresponds in the thousands and hundreds digits to that of the called line. For example, called line No. 4:692 may be reached only in the following manner:

A first selector selects one of a number of trunks numbered 4000 and is thereby connected with the second selector associated 1920. Serial No. 881,128.,

with the selected trunk. Throu h this second selector, access may be ha to all the lines the number of which is between 4000 and 4999. The second selector is then operated to select one of a number of trunks bearing the proper hundredsdigit; that is to say, a trunk numbered 4600. This trunk leads to a connector in which terminate lines 4600-4699. By operating the connector in accordance with the tens and units digits of the called number (9 and 2), the called line is selected.

In order to select any one of the ten thousand lines, one first selector is necessary to select a certain one of ten trunks and an associated second selector, through which access may be had to the desired thousands group; each of ten second selectors mustv have access to trunks bearing the ten different hundreds designations within the thousands group of the second selector; and the one hundred connectors associated with these trunks must each be arranged to select a the desired subscribers line, the thousands and hundreds numerical designation of which has been determined by the selection of a particular second selector trunk and a particular connector trunk.

As is well known, one first selector, ten second selectors and one hundred connectors could not handle more than one connection within a thousands group or digit at a time. In order to take care of the usual traffic of a telephone system, the number of selectors and connectors, and thus the number of their interconnecting trunks, must besufiicient to handle a maximum number of simultaneous calls initiated in the exchange. That is to say, a plurality of trunks and second selectors must be provided through which access may be had to a certain thousands group of subscribers lines, and a plurality of trunks and connectors must be provided to render accessible a certain group of one hundred subscribers lines. For this reason, the first and second selectors are arranged to performsecondary movements to select or choose an idle one of the selected group of trunks.

The factors that determine the total number of selectors, connectors and associated trunks depend, first of all, on the probable number of simultaneous calls that will have to be established-within the exchange. The number of such switches and trunks will be further dependent on the probable average holding time of a trunk or selector, i. e., the probable time for which a trunk or switch will be held busy during the establishment of a connection; the probable number of calls that will be abandoned prior to the completion of the connection; etc. On the theor of probabilities, the total number of switc ms and trunks may be determined from the above mentioned and other conditions.

Assuming now that in calculating the traffic of the whole exchange, we decide that 600 second selectors and associated trunks and 540 connectors and associated trunks are necessary. These are the figures we obtain when considering the trafiic of the telephone exchange as a whole, and their meaning is that a maximum of 540 simultaneous calls will be established in the exchange and, in addition to these, sixty calls will go only as far as the second selectors.

However, in some of the systems heretofore known, not the trafiic of the telephone exchange as a whole, but the trafiic of relatively small subdivisions of the telephone exchange must be considered-in determining the total number of selectors and trunks. This is so, because only through certain selectors, connectors and associated trunks may access be had to certain subscribers lines. It is possible to operate the systems of the prior art in a manner to permit the calling subscriber to appropriate any one of the first selectors for use because any called line may be reached through any first selector. But beyond the first selector, the traffic is definitely subdivided according to its destination. By operating the first selector to select a trunk and associated second selector bearing a certain numerical designation (e. g. 4000). the simultaneous calls directed towards the other nine groups of one thousand lines do not afiect the calculations to determine the size of the group of trunks and associated group of second selectors through which access may be had to subscribers lines 4000 to 4999. The probable number of simultaneous calls, average holding time and other factors that were considered in calculating the size of the second selector trunk groups, will vary in the ten groups. As' above stated, if the traffic of the whole exchange is considered. then 600 second selector trunks are sufficient. However, the smaller the group the greater the deviation within the oup from the average for the whole. In other words, the probability of (e. g.) 50% deviation from the average number of simultaneous calls into a particular thousands group is much greater than of a 50% deviation from the average number of simultaneous calls in the exchange as a whole. In flipping acoin, the average will be 50% tails and 50% heads. The larger the nummeaese only a; group 2000, +a; group 600 600 0; group 9000, To b; etc., 1n-

stead of for each group. During other parts of the day or season, group 1000 will need +a I); group 2000, 0; group 4000, -a-'b,- group 9000, +c, etc.,

second selectors. The probability is that in each one of the ten groups there will be a deviation from the average for the whole exchange, and it is impossible to predetermine in which group and when thedeviation will take place upwards or downwards.-

For these reasons, instead of the trailic of the exchange as a whole, the trafiic towards each group of one thousand lines was taken into consideration in determining the size of each second selector trunk group, and thus the total number of second selectors. In any given group, during certain parts of the day this traffic will be larger, and during other parts of the day 600 w' Sufficient second selector trunks must be provided to permit access to the lines of each group during the busy as well as the idle periods of the day or month. Therefore,

such trafiic will be lower than or b trunks will not be sufficient to take care of the traflic of a group. b

trunks must be provided for the 4000 group, 1 +a second selector trunks for the 2000 or +a+ b trunks must be provided for each group. If we count the second selectors and associated trunks that must be thus provided for handling the trafiic of all the ten groups, we find that 600-Pa: are needed instead of 600, as would be the case if the traflic of the exchange as a whole could be considered.

The same considerations apply to the connector trunks. Here again, the tra-flic is subdivided, but in this case not only with respect to the trafilc of the whole exchange or the trafiic of the thousands group selected by the first selector. The second selector cannot select but a trunk of a certain thou sands and hundreds numerical designation. Due to the variations within and between the various groups, the total numberof congroup, etc.,

nectors and associated trunks will have to be 540 a2, instead of 540 as would be the case if the trafiic of the whole exchange could be considered. t

From the above it will be seen that, in the systems of the prior art, the number of trunks and associated selectors and connectors necessary for handling the probable trafiic of an exchange is larger than -1s necessary for the handling of the trafiic of the exchange as a whole. The total number of such trunks and selectors is dependent on the size of the trunk groups into which the traflic is subdivided, and this in turn depends on the capacit of the switching devices used. Notwit standing the obgections raised against switching devlces having a capacity of more than one hundred lines, such large switches were considered economical under certain circumstances, mainly on account of the possibility ofproviding relatively large trunk groups, which results in a lesser subdivision of the traflic. In one hundred point switches, giving trunk groups of 10, it might be necessary under certain tralfic conditions toprovide more than ten trunks for access to a. thousandsgroup. One-solution of such a situation would be to appropriate more than one group of ten trunks for access to the particular thousands group. In view of the fact that a group of such trunks could not be used for gaining access to more than one thousands group, waste of space and aparat-us results from such arrangements. ut even in this case the trailic was divided into relatively small groups.

It has been suggested to employ so-called overflow trunks for the handling of the ab normal traffic. The provision of such arrangements is costly and leads to considerable complications in the system.

In accordance with the present invention,

the number of the selectively operable switching devices, such as intermediate and final selectors and associated trunks, depends on the traific requirements of the whole exchange, notwithstanding the fact that the capacity of the devices is relatively small. For instance, in calculating the number of second selectors and connectors and associated trunks to be provided, only the trafiic conditions of the exchange as a whole need be considered, and the trunks, if arranged in ac cordance with the present invention, will be much more efiicient than the necessarily larger number of trunks of a similar exchange, in which the traflicis subdivided into groups. Considering the above example, 600 second selectors and 540 connector trunks need only be provided in the present system.

Generally stated, the above-mentioned result is attained by routing a call through a trunk corresponding in numerical designation to certain digit or digits of the number of the called line, if such trunk is available. If this trunk is busy, then the selector arranged in accordance with the present invention does not hunt for an idle trunk bean ing the numerical designation corresponding 7 to that of the called line, and thus limits to a particular group the accessibility of a line.

The selector performs its hunting operation The invention may be applied at any point of the selective stage. It is applicable to systems of all sizes, including multi-ofiice systems, and in which selector switches of any well-known type are utilized. No at-' tempt has been made to. define the scope and the various features of the invention. This will be done in the appended claims. The above is merely introductory to the following general description of telephone systems in which the invention may be applied, and the detailed description of the circuits and apparatus of a telephone system embodying the invention.

In the drawings, Figs. 1, 2 and 3 represent as much of the circuits and apparatus of an automatic telephone exchange system as is necessary for a clear understanding of the details of a telephone system exemplifying the various features of the invention. Figs. 4, 5, 5 6 and 6 indicate a preferred scheme of numbering and wiring the terminal banks of first selectors, second selectors, and connectors.

General description.

Assuming a telephone system of the type considered in the above introduction, we find, for example, that, in view of all the trafiic and operating conditions of the exchange as a whole, 540 first selectors, 600 second selectors and 540 connectors are needed. These figures will, of course, vary, depending on the particular local conditions and the factor of safety used in calculating.

Any well-known means, such as line switches, line finders, relays, or any other automatically or manually operated devices may be used for connecting the callin line with the wipers of any one of a plurality of the 540 first selectors. In accordance with the present embodiment of the invention, the first selectors are of the well-known type (see Patent No. 97 7 ,536 to C. H. North) that perform first a primary or rotary and then a secondary or vertical movement to engage with their wipers anyone of the one hundred sets of terminals of which their respective banks, are composed. There are three deviations from the well-known structural arrangement of these. selectors: (1) The termiwipers of each nal bank comprises ten horizontal, but eleven instead of ten vertical rows of contacts; (2) the brush shaft may be moved twenty instead of ten vertical steps; and (3) each first and second selector is provided with two instead of one set of wipers. The two sets of selector (l44-147 and 144 447, Fig. 1) are multipled together. The two sets of wipers are rigidly mounted on the brush shaft, the set of wipers 144 147 being provided below the set 144-147 at a distance equivalent to the distance covered by the brush shaft in moving by ten vertical steps, Furthermore, the

lower wipers are displaced with respect to the upper wipers by one rotary step, whereby the former are always in line with the vertical row of contacts immediately to the right of the vertical row of contacts with which wipers 144147 are in alignment.

is illustrated in Fig. 4. In the present case,

both the thousands and the hundreds digit of the called number is determined in the first selector. The tens and hundreds digits remain undetermined at this stage of the selective operation, and for this reason, these digits are indicated by the letter X. The first vertical row of terminals serves for reaching trunks llXX, 12XX, 13XX, etc., lOXX; the second vertical row, for reaching the trunks 21XX2OXX, etc; and the tenth vertical row of terminals-for reaching the trunks O1XXOOXX. It will be noted that the numbering is always from 1-0. The eleventh vertical row of terminals leads to the same trunks as the first vertical row, these two rows being multipled together. In response to the thousands impulses sent out from the calling subscribers station, the brush shaft is rotated in a right-hand direction by a corresponding number of steps. Assuming that line #4692 is desired, the brush shaft of the first selector is rotated by four steps, bringing wipers 144147 in line with vertical row IV, one step below terminal 41XX, and the wipers 144-147 in line with vertical row V, eleven steps below terminal 51XX.

A change-over operation now takes place in the circuits of the first selector, and in response to the hundreds digit 6-dialed by the subscriber, the brush shaft of the first selector is moved by six steps in a vertical direction. The wipers 144147 pass over terminals 41XX, 42XX, etc., and in response to the sixth vertical step are brought into engagement with the terminals in which trunk #46XX terminates. The thousands and the hundreds digits of the number of this trunk correspond to those of the called number. The wipers 14 9 -147 are now five steps below terminal 51XX.

The trunk 46XX is now tested for its busy or idle condition. If the trunk is idle, then it is immediately seized by the first selector, and the calling line is extended through this trunk to the wipers of the second selector associated therewith. If the trunk is busy, then the first selector hunts J11 a vertical direction for an idle trunk.

Let us first assume that the trunk 46XX 1s idle, and that the first selector seizes the trunk terminating therein. This trunk terminates in the wipers of a mcond selector, the mechanical construction of which is exactly the same as that of the first selector. The numbering of the terminal bank of this second selector is shown in Fig. 5. It will be noted that the first terminal in the bank is 461K, and that the successive vertical rows, taken from left to right, comprise terminals numbered on a downward scale. Normally, the set of wipers, 244247 are one step to the left and one step below terminal 41X, and the wipers 244 -247, in line with vertical row 461X, eleven steps below terminal 461X.

In response to the seizure of the trunk termlnating in the wipers of this selector, 1t isrotated by one step, bringing wipers 244-247 in line with vertical row I, one step below terminal 461X, and wipers 244 5-247, in line with vertical row II, eleven steps below terminal 451K, The usual change-over operation takes place, and the second selector is ready to respond to the tens impulses. The nine tens impulses cause the wipers to' move in a vertical direction. Terminals 461X, 462X, etc., are successively passed, and in response to the ninth impulse, the wipers 244-247 rest in engagement with terminal 469K. The wipers 244 247 are now two steps below terminal 451K.

The trunk terminating in terminal 469K is now tested, and assuming that it is idle, the trunk and the associated connector are seized. The connector bank comprises only ten rows of terminals, and the brush shaft carrying a. single set of wipers is arranged toexecute only ten vertical steps. Otherwise, the connector is of the same construction as the first and secondselectors. The 'wipers 344'346 are normally one step to the left and one step below the first terminal in the bank. The numbering of this terminal bank is shown in Fig. 6.

Immediately upon the seizure of this connector, its wipers are rotated by one step and are thus brought one step below terminal 4691.' The connector is then ready to respond to the units impulses (2), the

change-over operation taking place immethe control of the units impulses, the connector wipers are moved in a vertical direction by' two steps, and are arrested in engagement with the terminals 4:692 in which the called line terminates. The ringing of the called party, the completion and restoration of the connection are then accomplished.

Let us assume now that neither the first nor the second selector finds idle the terminals of the first trunk encountered. In this case, when the first selector Wipers 144-147 find the trunk terminals 46XX busy, the brush shaft is automatically caused to continue its vertical movement. The wipers 144 147 successively test the terminals 47XX, 48XX, 49XX, 40XX, and assuming that all these terminals test busy, the brush shaft is caused to move by a further step in a vertical direction. The wipers 144147 now leave vertical row IV, and the wipers 144 14:7 enter into engagement with terminal 51XX. If this terminal is busy, the vertical movement of the first selector is continued until the Wipers 144 -147 encounter an idle set of terminals. Assuming that terminal 55XX is the first one idle, when the wipers encounter these terminals, the upward movement of the first selector is arrested, and the trunk terminating in these terminals is seized. It should be noted that the numerical designation of this trunk differs in both the thousands and the hundreds digits from that of the called line.

During this-trunk-hunting operation of the first selector, a register associated there-' with is caused to move its wiper 152 in a clockwise direction by as many steps as the first selector took in hunting for an idle trunk.

'The second selector associated with the trunk #55XX is of the same mechanical construction as the second selector associated with the trunk 46XX. However, the numbering of the terminal bank is different. The numbering of this bank is shown in Fig. 5. Immediately upon the seizure of the trunk, the second selector is caused to move its brush shaft by one rotary step, whereby the upper brushes are positioned in line with vertical row I, one step below terminal 551K, and the lower wipers in line with vertical row II, eleven steps below terminal 541K. Due to the off-normal position of the register associated with the first selector, the change-over operation cannot take place in the circuits of the second selector. The brush shaft of the second selector is caused now to rotate step-by-step (with the upper wipers below horizontal row of terminals I) and simultaneously the register moves its wipers step-by-step in a counter-clockwise direction. This operation continues until the register wiper reaches its normal position, when both the second selector and the register are arrested, and the change-over operation takes place in the circuits of the second selector.

The first selector took nine steps in hunt for an idle trunk. Therefore, the register was displaced by nine steps, and the second selector wipers were rotated by nine steps until the register wiper reached its normal position. For this reason, the upper wipers of the second selector are now positioned one ste below the vertical row 'X, the numbering of which is the same as that of the I row in Fig 5.

Under the control of the tens impulses, the second selector wipers are now caused to travel in a vertical direction to engage terminal 469X. Thus, notwithstanding the fact that the first selector chose a trunkof a diflerent numerical designation than the called line, the second selector was caused to re-route the call, and now the call is headed again towards the channel determined by the subscribers callin dial.

If the trunk with which the wipers of the second selector now make contact is idle, the above-mentioned connector is seized, and the call completed in the usual manner. Assuming, however, that trunk 469X is busy, the second selector is automatically operated to hunt in a vertical direction for an idle trunk. First, the upper wi ers of the selector engage terminals 460 and, finding these busy, the brush shaft is elevated by a further step, whereupon the upper wipers of the selector leave the terminals of vertical row X, and the lower wipers engage terminal 451X of row XI. The hunting operation continues until the lower wipers encounter a set of idle trunk terminals.

Assuming that terminals 453X are the first idle ones in this row, the second selector is arrested with its wipers in engagement with these terminals, and seizes the trunk terminating therein.

During the trunk-hunting operation of the second selector, the register associated with the first selector was stepped in synchronlsm with the second selector. The second selector having taken four steps to reach an idle trunk, the wiper of the register was also displaced by four steps from its normal position.

The connector associated with trunk 453X is of the same mechanical and electrical arrangement as the one associated with trunk 469K; however, the terminal bank of this connector is wired in accordance with Fig. 6. Upon the seizure of the trunk, the connector wipers are brou ht below terminal 4551, but the register eing off-normal, the change-over operation does not take place in the circuits. Under the control of the connector wipers are caused to rotate.

.- by two steps and into engagement with The register requiring four steps to be restored to normal, the connector wipers are rotated by four steps. This will bring the wipers .in line with vertical row V, which is the row containing the called line terminals. The change-over operation now takes lace, and under the control of the units impulses, the connector wipers are elevated the terminals of line #4692.

The call has reached its proper numerical destination, notwithstanding the fact that it was routed through trunks provided for access to lines of a diflerent thousands, hundreds and tens numerical designation. All this takes place Without any additional act of the operator or subscriber.

A pilot switch is associated with each first and second selector for controlling its circuits. These pilot switches may be of any well-known design, e. g., like the one disclosed in Patent No. 988,390 to F. Schoenwolf. The pilot switches are equipped with three pairs of wipers, angularly displaced in a {manner to permit-fine wiper of a pair to enter into co-operation with a row of terminals when the other wiper leaves the last ter minal in the row.

The register is composed of a circular row of contacts, with which a wiper co-operates. The wiper may be moved in a clockwise or counter-clockwise direction under the control of suitably arranged magnets.

The terminal banks of all the first selectors are numbered in the manner indicated in Fig. 4. The system used in multipling terminals of the first selectors depends on the total number of second selectors. 'The terminal banks of one hundred second se1ec tors accessible to one first selector are dif-' ferently numbered, that is to say, in no two of'such second selector banks will the trunk bearing the same numerical designation appear in the same place. The principle followed in the numbering of the terminal bank of the second selectors is the same as the one followed in the terminal banks illustrated in Figs. 5 and 5 The. first terminal in the I vertical row of each one of the one hundred second selectors, accessible to one first selector, serves for a trunk of a diiferent numerical designation. The other terminals in the I horizontal row are numbered by the same thousands digit but gradually decreasing hundreds digits until the hundreds digit 1 is reached. After this comes the terminalof the trunk of the next lowest thousands digit and the highest hundreds digit (0), and this is followed by the terminals of the trunks of the last mentioned thousands digit but gradually decreasing hundreds digits. The ten terminals within the same vertical row are .for trunks of the same thousands masses and hundreds digit, but for different tens digits.

The one hundred difi'erent second selector numberings will be apparent from the following list, in which the first and last terminal in horizontal row I- of each second selector is given:

In the assumed case ofa system in which six hundred second selectors are provided, one hundred selectors havingv differently numbered banks, the numbering ofsix sec- ,ond selectors will be the same but different from the other 594 second selectors. By dividing the total number of first selectors lectors will be multipled together.

messes (540) by the number oi second selectors serving trunks in the same order (6), we obtain the number of the first selector banks that must be multipled together. In the present case, first selector banks must be multipled together.

A preferred method of multiplin is as follows: Of the 540 first selectors, t e terminal llXX of the first ninety will be multipled together and connected to the wipers of a single one of the six second selectors, the banks of which are numbered like (1) of the above list. The terminal llXX of first selectors 91-180 are multipled together and connected to the wipers of the second one of the six second selectors numbered like (1). The wipers of the other four second selectors numbered like (1) are connected to the (multipled) terminals llXX of first selectors 181-270, 271-360, 361450, and 451540', respectively.

The trunking between the other first selector terminals and the second selector "wipers is on the same principle, but the terminals of different oups of first selectors are preferably mu tipled together. Terminals 12XX of first selectors 1l100 are multipled together and connected to the wipers of one of the six second selectors belonging to group 2. The wipers of the other five second selectors belonging to this group are connected to the multipled terminals, 12XX of first selectors 10l190, 191-280, 2s1 370, 371-160, and 4s1 540 10, respectively. The wipers of the six' second selectors numbered like (3) are connected respectively, to the multipled terminals 135X of first selectors 21 110, 111-200, 2( )1290, 291-:380, 381-470, 471-20.

The above trunking arrangement may be readily followed out for all the selectors and the result will be that the terminals of dissimilar but overlapping groups of first se- Other methods may be used in multipling the first selector. terminal banks. Terminal 12XX of three times ninety even number first selec-- tors may be connected to three second selectors numbered like (2). The wipers of the other three second selectors of the same-num bering may be connected to three times ninety odd number selectors.

In following out this lastmentioned system-of multipling, terminals 13XX of first selectors 3, 6, 9 267, 270 are multipled together and connected to the wipers of one second selector numbered like (3). Terminals 13XX of first selectors 273, 276 537, 540 will be connected in multiple to the wipers of another second selector like (3). Terminals 13XX of firs-t selectorsv 2, 5, 8 266, 269 will be connected in multiple to a third one of the second selectors (3). Ter- 1 minals 13XX of first selectors 272, 275 536, 539 will be multipled to the fourth second selector of grou (3). Corresponding terminals of first se ectors 1, 4, 7 265, 268 w1l l be multipled to the fifth second selector like (3), and terminals 13XX of first selectors 271, 274, 277 535, 538 to the sixth second selector of this group. The other terminals will be multipled by skipp1ng 4, 5, 6, etc., first selectors.

Such merged multipling of the first selector banks is particularly advantageous in case, by some chance of the trafiic or of the call distribution circuits, a group of first selectors might average busier than another. Where the call distribution to the first selectors is practically perfect, there is no advantage in. such merging of dissimilar groups of trunks. As far as the present invention is concerned, it is wholly independent of the method of multipling the first selector terminals. In the present case, for instance, all the terminals of the first selectors may be wired in the same manner as the terminals llXX, the number of first selectors being without any efi'ect upon the number of second selectors and connectors. As above stated, the number of the latter is calculated directly from the busy hour average simultaneous calls put up to them irrespective of the method of trunking the calls to the second selectors.

The second selectors have access to dis similar but overlapping groups of trunks, and for this reason the probability of a first selector finding an idle second selector is greater than if the second selectors had access to entirely separate groups of trunks. Furthermore, due to the fact that the second selectors have access to trunks belonging to different numerical groups of trunks, the first selector also may be permitted to hunt for a second selector of any one of a plurality of numerical groups. In some of the systems of the prior art, as soon as the first selector is operated in accordance with the thousands digit of the called number, it cannot hunt but for a second selector through which access may be had only to this same thousands group of lines. At this particular time, more than the average number of simultaneous calls may be directed towards this particular group of thousand lines. To take care of this trafiic, more than the average number of second selectors had to be provided for this group. In the present system, the first selector may extend a call in accordance with the thousands digit of the called number or in accordance with another thousands digit and still reach the line of the desired thousands designation. If excessive traffic is'directed at this particular time towards the lines of the desired thousands digit, the first selector may select a trunk and associated second selector through which normally calls directed to another thousands group of lines pass. The probabilities are that in no two groups will there be an abnormal traffic at the same time. Another advantage of the present method of arranging the trunks served by a selector resides in this; that, whereas in some of the systems of the prior art if all the terminals of a selectoraccessible during its secondary movement are not necessary for handling the trafiic, the other terminals were useless; in the present system all the terminals accessible during a secondary movement are used irrespective of the number of trunks provided for the handling of the average trafiic. Taking, for example, the socalled hundred point switch, one hundred sets of terminals had to be installed whether the traflic required one hundred or only sixty terminals. The other terminals were left to accumulate dust. With the present system of'numbering, all the one hundred terminals may be used irrespective of the trafiic requirements. One and the same terminahmay be selected, once in response to a numerical operation of the selector, and at another time in response to a hunting oporation of the selector. Due to this constant and probably uniform use of the terminals, the terminals will automatically be keptclean of dust and thus their electrical conductivity will not be impaired. In the systems of the prior art, not used or only seldom used, terminals must be constantly dusted by manual labor.

Similar advantages are attained by the use of second selectors and connectors arranged in accordance with the present invention. In this case the advantages are realized in connection with the hundreds instead of the thousands groups.

The terminal banks of all the, connectors of the present system will be differently numbered. The numbering is on the same principle as the one used in Figs. 6 and 6 The following is a list of the. first and last terminals in the horizontal row I of some of the one thousand connectors, (for the sake of c-learness, the connectors are here divided into ten groups, A-J, of one hundred connectors) A 20. 2011-3121 1. 1111-1221 p 21. 3111-3221 2. 1211-1321 3. 1311-1421 80. 3011-4121 1. 1411-1521 31. 4111-4221 5. 1511-1621 6. 1611-1721 40. 4011-5121 7. 1711-1821 8. 1811-1921 50. 501 -6121 9.1911-1021 10. 1011-2121 60. 6011-7121 11. 2111-2221 i 13. 2211-2321 70. 7011-8121 a a a =1= B F V 1. 1121-1231 1. 1161-1271 2. 1221 1a31 s a. 1321 1431 100. 0061-1171 1. 1121-1531 5. 1521 1e31 G s0. s021--9131 1. 11s1 1291 I '3 =1 #1 I 100. 0021-4131 I 0 1.1191-1201 I v a a a 1. 1131-1211 31. 1191-4201 2. 1231-1311 a ae.4e91 .1701 10. 1031-2141 I 1. 114.1 1251 50. 5001 c111 2. 1211 1351 r In the present case, we need only 540 connectors, and for this reason 460 combinations will be omitted. All the similarly numbered terminals of all the second selectors are multipled together and connected to the wipers of the connector, the lower left-hand terminal 01" which corresponds in thousands, hundreds and tens numerical designation to that of the connected second selector terminal. If the particular connector has been omitted, a permanent bus guard is placed on the multiple wire. en the second selector wipers encounter such permanently busied terminal, the will automatically hunt for another terminal as though the terminal was rendered busy by another selector.

As above mentioned, theinvention is not limited to selector andconnector switches of the articular structure disclosed. For example, if the invention is applied with witches performing their primary motion in a vertical and their secondary motion in a horizontal direction, the wipers should be mounted on the brush shaft in such a manner that one set is in line with a horizontal row of terminals below the horizontal row with which the other set of wipers is in alignment, and enter into engagement with the first terminal of its row when the other set leaves the last terminal of the row with which it co-operates.

Various methods for embodying the invention into systems utilizing switches of the mentioned types, or switches that perform motions only in a rotary, only in a vertical or in two more planes will readily suggest themselves to those skilled in the art.

The present exemplification of the invention is so provided that a first or second selector can select only one out of ten idle trunks in extending a call. The limiting of the hunting movement of selectors to ten terminals has been found sufficient even in systems utilizing the usual grouped system of trunking, and will be more than sufiicient in the present system. If, however, it is required toextend the hunting range of a selector, this may be readily accomplished by increasing the size of the terminal banks, changing the system of numberin in ac cordance with the principles herein disclosed, providing more than two sets of brushes to cooperate with the various rows of the terminal bank of a selector, etc. The invention is applicable to full automatic as Well as automanual or semi-automatic systems.

The particular construction or arrangement of the pilot or side switches and register switch is immaterial and the two may be combined into one structure. Furthermore, the register may be provided elsewhere than in association with the first selector. For instance, in semi-automatic systems, the function of the register should be .preferably accomplished by some means associated with the operators impulse controlling mechanism or sender. Operators revertive impulse senders used in conjunction with so-called power-driven systems are particularly adapted for taking care of this impulse registering operation.

Detailed description.

primary control apparatus disclosed in the mentioned patent to H. G. vWebster, No. 1,252,974, patented January 8, 1918. Under the control of this apparatus, the relays 103 and 104 are energized to extend the calling line to an idle trunk leading to the first selector. Upon the actuation of relays 103 and 104, a circuit is closed from ground through the winding of slow-acting relay 105, relay contacts'l03 and 104, the calling line circuit, the apparatus at the calling station, relay contacts 104" and 103*, and the winding of relay 112 to rounded-battery. The relays-105 and 112 gecome energized. The relay 105 closes a circuit from ground through its armature and front contact, and then in arallel through resistances 103 and 10 re ay contacts 103 and 10 1, the windings of relays 103 and 104 to grounded battery. Under the control of these circuits, the switching relays 103 and 104 are locked up. Another circuit closed upon the extension of the line to the first selector may be traced from grounded battery, through the winding of cut-off relay 102,'relay contacts 104 and 103, and the winding of relay 111 to round. These relays become energized, an the closure of this circuit causes the changing of the electrical potential on the multiple calling terminals of the line in a manner to prevent its seizure. The. relay 102 opens the circuit of relay 101, whereupon the primary control apparatus is actuated in a manner disclosed in the mentioned patent -to H. G. Webster.

The energization of the relays 111 an 112 results in the closure of the following circuits: from. ground through the righthand armature and front contact of relay 111, the left-hand armature and front con- T housamls selection.

The subscriber proceeds now to operate his dial 100 in accordance with the numerical designation of the called line. First, the thousands'impulses are produced by interrupting the line circuit a number of times equivalent in numerical designation to the corresponding digit of the called number. In the present case, four such impulses areproduced. In response to each interruption of the circuit, the relay 112 releases its armatures, but the relay 105 being sluggish, maintains its armatures attracted during the sending of the impulses. Upon the first release of the armatures of relay 112, the relay 113 and the magnet 130 become de'energized. Upon the de-energization of magnet 130, the pilot switch arms 131, 132 and 133 are stepped by one step to cause their respective wipers to engage the second set of contacts. Upon the following closure of the line circuit, the relay 112 again attracts its armatures. These circuit closures during the sending of the impulses are of a relatively short duration, and the relay 113 is not traversed by current for a suflicient length of time to permit it to attract the retarded armature. However, the rotary magnet 141 is energized by the first short closure of the line circuit, the current path being traced from ground through the right-hand front contacts of relays 111 and 112, the #2 contacts co-operating with arm 131, wipers 131 and 131*, and the winding of magnet 141 to grounded battery.

Upon the following (second) break of tne line circuit and the consequent de-ener iz ing of relay 112, the rotary magnet 141 comes de-energized and moves wipers 144-147 and 144*147 of the first selector by steps in a horizontal plane. The second inner contact of the bank served by pilot arm 131 is not connected to the winding of magnet 130. For this reason, the last mentioned and the subsequent operations of the relay 112 do not affect this magnet. Upon the second reclosure of the line circuit, the relay 112 again closes the circuit of magnet 141. Under the control of the following two circuit interruptions and closures, the relay 112 operates the magnet 141 over the above traced circuit, and this magnet rotates the wipers of the first selector by two additional steps.

The fourth (last) interruption of the line circuit is followed by a relatively long closure of the circuit, permitting the energization of the relay 113. This relay closes a circuit from grounded battery through the winding of magnet 130, the armature and front contact of relay 113, the normally closed contacts of this magent, and the #2 contacts engaged by wipers 132 and 132 to ground at the eft-hand front contact and armature of relay 111. The magnet 130 becomes energized, interrupts its own circuit and causes thus the stepping of the pilot switch wipers into engagement with their respective third sets of contacts. When magnet 130 shifts wipers 131 and b from the #2 contacts to the #3 contacts, the circuit to the magnet 141 is interrupted and this magnet becomes deenergized. The wipers 144-147 are moved by an additional step, the total number of steps corresponding to the thousands digit dialed. The wipers 144147 are now below terminals 41XX' (Fig. 4). As soon as pilot wipers 131 a and b engage the #3 terminals, the magnet 130 is again energized, the relay 112 being energized over the re-established line circuit.

H undreds selection.

The calling subscriber produces now the six hundreds impulses. In response to the first interruption of the line circuit, the relay 112 is again de-energized, and by releasing its armatures, causes the de-energization of the relay 113 and the magnet 130. The magnet 130 moves the pilot switch wipers into engagement with the fourthset of contacts. The relay 113 remains de-en ergized during the sending, of the hundreds impulses. Upon the subsequent closure of the line circuit, the relay 112 becomes energized and causes the energization of the vertical magnet 142, the circuit being closed from grounded battery through the winding of magnet 142, pilot wipers 131 a and b, and the right-hand armatures and front contacts of relays 112 and 111 to ground.

The second interruption of the line circuit I results in the de-energization of the relay 112, whereupon the magnet 142 becomes deenergized and moves the wipers of the first selector one step in a vertical direction. Upon the succeeding shortv closure of the line circuit, magnet 142 is again energized, and upon the third interruption of the circuit of relay 112, the magnet 142 is de-energized for the second time to lift the wipers to the second level. Relay 112 continues to control magnet 142 in accordance with the interruftions and closures of the line circuit. 11 response to the sixth opening of the line circuit, the magnet 142 lifts the wipers by the fifth step. Upon the relatively long closure of the line circuit following the sixth interruption, the relay 113 is again caused to attract its armature.

During the sending of the hundreds impulses, a relay 114 was maintained energized by current from ground through pilot wipers 132 and 132?, and the winding of relay 114 to grounded battery. Through its righthand armature, the relay 114 closed an energizing circuit for relay 115. When the relay 113 becomes energized, it closes a circuit from grounded battery through the winding of magnet 130, the armature and front contact of relay 113, the normal contacts of 130, the left-hand armature and front contact of relay 114, and the pilot wipers 132 a their wipers into engagement with the #5 set of contacts. The wipers 131 a and b leaving the #4 contacts cause the de-energization of magnet .142. IThls magnet moves the first selector wipers by a. sixth vertical step into enga ement with the terminals of trunk 46X (Fig. 4). If the second selector to which this trunk leads is idle, then the trunk is immediately seized for use. If, however, this trunk is busy, and this is the condition we will assume, the first selector hunts for an idle second selector trunk.

Hun-ting for idle second selector.

When the pilot arm 132 is moved out of engagement with the #4 set of contacts, the relay 114 becomes de-energized, but the slow-acting relay 115 retains its armatures attracted for a brief period of time. If the selected trunk line is busy, then, as will be set forth in detail, the terminal with which the test wiper 146 of the first selector contacts is connected to ground. For this reason, a circuit is closed from ground through the wiper 146, the right-hand armature and back contact of the relay 114, the left-hand armature and front contact of relay 115, and the winding of relay 116 to grounded battery. The relay 116 becomes energized, and closes a locking circuit for itself through its right-hand armature and front contact and the test wiper 146.

The relay 115 becomes now de-energized. A circuit is closed from grounded battery through the winding of the vertical magnet 142, the left-hand front contact and armature of the relay 116, the normal contacts 154 of the register magnet 150, wipers 132 and 132 andthe left-hand front contact and armature of relay 111 to ground. The magnet 142 becomes energized, and closes a circuit from ground through its armature and front contact, wipers 1131 and 131, and. the winding of register magnet 150 to grounded battery. The magnet 150 becomes energized, and by opening its contacts 154 causes the de-energization of the magnet 142. The wipers of the first selector are stepped by one vertical step. Upon the opening of the contacts of the magnet 142, the magnet .150 becomes de-energized, closes contacts 154,

and moves register wiper 152 into engagement with contact #1. If the contact engaged b the wiper 146 is grounded, indicating that the selected trunk is busy, the relay 116 is maintained energized, causing the repetition of the above described operation of magnets 142 and 150.

Assuming that all the trunks terminating in the No. IV vertical row (Fig. 4) are busy, the wipers 144-147 engage in suc cession contacts 46XX, 47XX, 48XX, 49XX, and 40XX. The contacts 40XX being busy, the wipers are moved by a further step. The wipers 144'147 are now out of engagement with the IV vertical row of terminals, but the wipers 1444-147 engage terminals 51XX of row V. The locking circuit of relay 116 is controlled through test wiper 146", and the hunting operation continues until the wiper 146 encounters a non-grounded terminal Assuming that the first row V are also busy and the terminals 55XX are idle, when the latter are reached, the relay 116 becomes deenergized, preventing the further operation of magnets 142 and 150. The magnet 150 caused the movement of wiper 152 by as many steps as the wipers of the first selector took in hunting for an idle trunk. That is to say, the register wiper 152 is in engagement with contact #9. A circuit is closed from ground through the left-hand armature and front contact "of relay 111, the wipe-rs 132 and 132", contact 154 of magnet 150, the left-hand armature and back contact of relay 116, the right-hand inner armature and back contact of relay 115, the normally closed contact of magnet 130, the front, contact and armature of relay 113, and the winding of magnet 1.30 to four terminals in grounded battery. The magnet 130 becomes Correcting operation;

Upon the energization of the relay 207, first a circuit is closed from grounded battery through the winding of rotary magnet 241, the left-hand armature and back contact of relay 208, pilot wipers 231 and 231, the right-hand armature and front contact of relay 207, and the right-hand rotary offnormal contacts 214 to ground, The magnet- 241 becomes energized and closes an energizing circuit for relay 208. The latter attracts its armatures, opening the magnet circuit and closing a circuit for slow-to-release relay 209. The relay 209 becomes energized and remains in that condition during the subsequent vibration of the armature of relay 20S. Upon the de-energization of magnet 241, the second selector wipers are rotated by one step and below terminals 551K, and the relay208 is de-energized. The right-hand contact of rotary off-normal contacts 214 is opened and the left hand" contact closed. A circuit is now closed from ground through the winding of'magnet 15 1, Wiper 152, the contact #9 engaged by this Wiper, the right-hand outer armature and back contact of relay 116, wiper 147, the right-hand armature and front contact of the relay 207, the wipers 231 and 231 of pilot switch arm 231, the left-hand armature and back contact of relay 208, and the winding of rotary magnet 241 to grounded battery. The magnets 241 and 151 become energized. The rotary magnet 241 closes a c1rcuit from ground through its front contact and armature, and the winding of relay 208 to grounded battery. The relay 208 becomes energized, and by opening the circuit of th magnets 241 and 151 causes its own de-ene gization. The magnet 241 moves the wipers of the second selector by a second step in a rotary direction, and the magnet 151 moves the wiper 152 of the register b one step in a counter-clockwise dlrection. pon the de-energization of the relay 208, the

mentioned circuit including magnets 151 and 241 is again closed, and the operation of these magnets is repeated, until, after being moved by nine steps, the register wiper 152 reaches its normal contact. The rotary magnet 241 of the second selector is thus caused to operate this selector first by one step and then by a number of ste s equivalent to the number of steps by which the register wiper has been displaced (nine) in response to the hunting action of the first selector. The wipers of the second selector are now below 1 terminals 461K (Fig. 5) corresponding in the thousands and hundreds digits with the number dialed by the calling party.

As soon as the second selector is displaced from its normal position and actuates the oif-normal contacts 214, a circuit is closed from ground through these contacts, the pilot switch wipers 233 and 233", thefront contact and armature of the relay 209, and the winding of the pilot switch stepping magnet 230 to grounded battery. This magnet becomes energized. When the relay 209 becomes de-energized upon the permanent de-energization of the relay 208. the magnet 230 becomes deenergized and moves the arms 231, 232 and 233 by one step to cause the engagement by their wipers of the #2 sets of co-opera-ting contacts. A circult 15 now closed from ground through the righthand-armature and. front contact of relay 111, the right-hand armature and front contact of relay 112, wipers 131"6 and 1316, selector wiper 144 wipers 231-2 and 231 -2, and the winding of magnet 230 to grounded battery. This magnet becomes energized.

Tens selection.

The calling party produces now nine impulses representing the tens digit of the called number. Upon the first interruption of the line circuit, the relay 112 opens in its right-hand front contact the circult of magnet 230, whereupon the pilot switch controlled by this magnet is moved into the third position. In its left-hand front contact, the relay 112 opens the circuit'of the slow relay 113. This relay becomes de-energized and remains in that condition during the sending of the tens impulses. Upon the de-energization of relay 113, a circuit is closed from grounded battery through the winding of ma et 130, the armature and back contact 0 this relay, and the pilot wipers 132 -43 and 132 6 to ground. The magnet 130 is energized. As soon as arm 232 reaches position 3, a circuit is closed from ground through the wipers 2323 and 232"-3, and the winding of relay 211 to grounded battery. Relay 211 becomes energized.

Upon the subsequent closure of the line circuit, the rela 112 connects round through its rightand armature an front contact, pilot switch wipers 131 6 and 131 6, selector wiper 144*, pilot switch wipers 2313 and 231" 3, and the winding of vertical magnet 242 to grounded battery. The vertical magnet becomes energized, and closes a circuit from grounded battery through its lower armature and front contact, and the winding of relay 210 to ground. This relay becomes energized and closes a circuit from battery through its right-hand armature and front contact, and the winding of a slow relay 213 to ground at rotary off-normal contact 214. During the subsequent vibration of the armature of relay 210 under the control of the vertical magnet 242, the relay 213 maintains its armatures attracted. The magnet 230 is held energized through a circuit including the lower armature and front contact of relay 213.

Upon the second interruption of the line circuit, the magnet 242 is de-energized, and moves the wipers of the second selector by one step in a vertical direction. Under the control of the following eight impulses, the vertical magnet 242 elevates step by step the wipers of the second selector. In response to the last (ninth) interruption of the line circuit, the wipers 244-247 will have been elevated by eight steps. closure of the line circuit, the magnet 242 becomes energized and the relay 113 is permitted to attract its armature, whereupon the magnet 130 becomes de-energized and moves its associated pilot arms into position 7. The circuit of the vertical magnet 242 is now interrupted. This magnet becomes de-energized and causes the second selector wipers to take a ninth vertical step. The wipers of the second selector are now in engagement with the terminals of the trunk #469X. The relay 210 is now de-energized and causes the de -energization of relay 213.

Upon the last long i This relay in turn opens the circuit of mag net 230, whereupon the ilot arms are moved into position 4.

Hunting for idle connector.

If the trunk with which the wipers of the second selector are now in engagement s busy, then ground is connected to its multiple test terminals. Assuming this to be the case, the relay 211 does not become de -energized when the associated pilot switch moves out of position 3, because a locking circuit is closed through the right-hand 1nner front contact and armature of this relay, the right-hand armature and baclr contact of relay 209, and the selector w1per 2 46. As soon as the pilot switch reaches position 4, a circuit is closed from grounded battery through the Winding of vertical magnet 242, the left-hand back contact and armature of the relay 210, the left-hand front contact and armature of relay 211, pilot wipers 231 -4 and 231 -4, and off-normal contact 214 to ground. The magnet 242 becomes energized and closes two circuits; one from grounded battery through its lower armature and front contact, the winding of relay 210, to ground; and the other from ground through its upper front contact and armature, pilot wipers 232 4 and 232 -4, wiper 145 of the first selector, pilot wipers 131 7 and 131 --7, and the Winding of register magnet 150 to grounded battery. The magnet 150 and the relay 210 become energized. In its left-hand back contact, the relay 210 opens the energizing circuit of the magnet 242, and in its right-hand front contact the relay closes an energizing circuit from grounded battery, through the winding of relay 213, and off-normal contact 214 to ground. Upon the de-energization of the magnet 242, the relay 210 becomes de-energized and the wipers of the second selector are displaced by one step in a vertical direction. In its upper front contact, the magnet 242 opens the energizing circuit of the magnet 150. whereupon this magnet becomes de-energized, and moves the register wiper 152 into engagement with its #1 contact. Upon the energization of the relay 213, a circuit is closed from grounded battery through the Winding of magnet 230 and the lower armature and front contact of relay 213 to ground. This magnet becomes energized. As above stated, during the vibration of the armature of relay 210, the relay 213 maintains its armatures attracted.

If the trunk with which the selector wipers are now in engagement is busy, the locking circuit traced through wiper 246 maintains the relay 211 energized. For this reason, the circuit of magnet 242 is again closed, resulting in the repetition of the above described operations for moving the wipers of the second selector and the the wipers 244247 leave the #X vertical,

row of terminals and the wipers 244247. begin to hunt through the #X1 Vertical row of terminals. Assuming that three additional steps are taken before an idle trunk terminal is reached, when the wiper 246 encounters the test terminal of an idle trunk #453X, the relay 211 becomes deenergized and causes the opening of the circuits of magnet 242 and rela 210. Shortly after the de-energization o relay 210, the relay 213 becomes de-energized. Upon the deenergization of relay 213, the magnet 230 becomes de-energized and moves the associated pilot arms into position 5. The second selector having taken four steps to reach an idle connector trunk, the register wiper 152 will be in engagement with terminal #4.

The relay 211 closes a circuit from ground through its right-hand inner armature and back contact, the right-hand back contact and armature of relay 209, wiper 246, and the winding of relay 312 associated with trunk #453X to grounded battery, for energizing this relay. This ground being applied to the multiples of the test terminal of this trunk, the seizure of the trunk by another second selector is prevented. The connector wipers are now rotated one step. A circuit is closed from grounded battery through the winding of rotary magnet 341,

left-hand contacts of relay 313, rotary offnormal springs 320, and the inner righthand contacts of relay 312 to ground. Mag net 341 closes an energizing circuit for relay 313 and the latter opens the circuit of magnet 341. Upon the de-energization of magnet 341, the relay 313 becomes de-energized. The connector cannot be further rotated under the control of this circuit because of the opening of contacts 320 upon the rotary displacement of the connector. The connector wipers are now below the terminals of line #4531 (Fig. 6).

Uponthe energization of the relay 313, the relay 314 becomes energized. This relay is of the slow-to-release type and maintains its armatures attracted for a short period of time after the de-energ'ization .of relay 313. Before the relay 314 had time to release its armatures, a circuit is closed from grounded battery through the winding of magnet 341, the left-hand back contact and armature of relay 313, the left-hand armature and front contact of relay 314,"

211, the ri ht-hand armature and front contact of re ay 207, first selector wiper 147, the outer right-hand contact and armature of relay 116, the contact #4 of the register, wiper 152, and the winding of magnet 151 to ground. The magnets 151 and 341 become energized. The magnet 341 closes a circuit from ground through its armature and front contact, and the winding of relay 313 to grounded battery. This relay becomes energized and again closes the circuit for slow-to-release relay 314 to maintain it energized. In its left-hand back contact, the relay 313v opens the circuit of magnets 151 and 341, and these magnets cause, respectively, the displacement of register. wiper 152 by one step in a counter-clockwise direction, and the displacement of the connector wipers by a second step in a rotary direction. The relay 313' is again energized and this operation continues until the register wiper 152 reaches its normal position, the connector being rotated by as many steps (four) as is required to restore to normal the register. While the relay 313 is vibrating its armatures under the control of magnet 341, the slow-acting relay 314 maintains its armatures attracted. When the register wiper 152 reaches its normal position, the circuit of magnets 151 and 341 IS permanently opened and the relay 313 becomes tie-energized. Relay 314 is now de-energized. The connector wipers, having successively engaged terminalsof lines Nos. 4521, .4511, 4601, are now in engagement with the terminals of line No. 4691 (Fig. 6).

Sending of the units impulses.

The calling subscriber proceeds now to send the two units impulses. The relay 112 vibrates its armatures in response to the interruptions and closures of the line circuit. Upon the first de-energization of this relay, the relay 113 becomes de-energized and remains in that condition during the sending of the impulses. Magnet 130 is also de-energized by the opening of the righthand contact f relay 112. This magnet was energized as soon as the pilot switch reached position 7, by current flowing from grounded battery through the winding 130, pilot wipers 132 7 and 132 7 and the right-hand front contacts and armatures of relays 112 and 111 to ground. The pilot switch now shifts its wipers to the 8th position. An energizing circuit is closed for magnet 130 from ground through the lefthand inner armature and front contact of relay 111, the pilot wipers 132a and b8, the back contact of relay 113, and the winding of magnet '130 to grounded battery.

Upon the subsequent closure of the line circuit, the relay 112 becomes energized and closes a circuit that may be traced from ground through the right-hand armatures and front contacts of relays 111, 112, pilot wipers 131 -8 and 131 -8, first selector wiper 144, the upper back contact and armature of the relay 213, second selector wiper 244, the left-hand contact of relay 312, rotary off-normal contact 322, the righthand armature and back contact of relay 314, and the windin of magnet 342 to grounded batter-1y. is magnet becomes energized and c ses through its armature and front contact an energizing circuit for relay 315. Upon the subsequent interruption of the line circuit, the magnet 342 becomes de-energized under the control of the relay 112, and moves the connector wipers by one step in a vertical direction.

Upon the following last closure of the line circuit, the relay 112 becomes permanently energized. The magnet 342 is again energized, and somewhat later, the slow-to-pullup relay 113 becomes energized. In its back contact, the relay 113 opens the circult of magnet 130, whereupon the latter becomes deenergized and permits the pilot arms to escape into the ninth position.

When the pilot wipers 131a and I) leave their eighth contact, the above-traced circuit for magnet 342 is opened in these contacts. The magnet 342 becomes deenergized and moves the connector wipers b a second step in the vertical direction. T e connector wipers are now in engagement with the terminals of line No. 4692. The relay 315 releases its armatures shortly after the last deenergization of magnet 342.

If the called line is idle, then, as will be set forth more in detail, full battery potential exists on its test terminal, permitting the energization of marginal test relay 316 through the following path: grounded battery through the winding of the cut-off relay 102 of the called line, test terminal and connector test wiper 346, the right-hand back contact and armature of relay 315, the high resistance left-hand winding of the relay 316, and vertical off-normal cont-act 325 to ground. The relays 102 and 316 become energized. The relay 316 locks up through its low resistance right-hand winding, outer righthand armature and front contact and the above-traced circuit through the winding of the cut-off relay. Due to the closure of this path, the electrical potential on the multiples of the test terminal is reduced so as to prevent the energization of another test relay like 316 in response to its connection with this line by its associated connector switch. The relay 316 closes a circuit through its right-hand outer armature and front contact for energizing relay 318, and a circuit from ground through interrupter 333, its inner-right-hand armature and front contact, the lower back contact and armature of relay 330, and the winding of relay 332 to grounded battery. This relay is 

